Couldn't talk about politics (or have political opinions),
sports,
certain popular books or TV shows,
the pursuit of secular education,
telling off-color jokes,
saying how boring are JW meetings and field service.
Couldn't "elevate" yourself above others by talking about how well you were doing at your job or profession or any skill basically!
Also could certainly never recommend a certain "practice" (which they termed 'self-ABUSE'!!) as a wonderful way to help you sleep or relax...